Mirror construction



Dec. 6, 1932. 0. 1.. SHATTO ETAL 1,890,166

.HIRROR CONSTRUCTION Filed April 5. 1930 INVENTORS DA we 1.. sun r10 men/Yr Harp 40mm:- 4507' THE/,4? ATTORNEY Patented Dec. 6, 1932 UNITED STATES PATENT OFFICE DAVID L. SHAT'IO, OF BERKELEY, AND FRANK FLOYD LINDSTAED'1,OF OAKLAND, CALI- FOBNIA, ASSIGNOBS 'IO HERCULES GLUE COMPANY, OF SAN FRANCISCO, CALIFORNIA,

A CORPORATION OF CALIFORNIA MIRROR CONSTRUCTION Application med April 12 1980. Serial No. 441,824.

Our invention relates to a beam structure including sheet glass, and the primary ob ect of our invention is the provision of reinforcing means for a mirror to prevent bowing thereof, and consequent distortion of. the image.

Another object of our invention 15 the provision of such reinforcing means, which Wlll allow the use of glass of less thickness than necessary if the reinforcing means were not used, thereby effecting an economy in the cost of the glass.

The invention possesses numerous other objects and features of advantage, some of which, with the foregoing, will be set forth in the followin description of our invention. It is to be un erstood that we do not limit ourselves to this disclosure of species of our invention, as we may adopt variant embodiments thereof within the scope of the claims.

Referring to the drawing:

Figure 1 is a perspective view illustrating a corner portion of the mirror construction of our invention.

Figure 2 is a plan view of the underside of our mirror construction; illustrating a modified construction. A portion of the structure is omitted to shorten the view.

Figures 3 and 4 are elevational views illustrating methods of mounting our mirror construction. Portions of the structures. are shown in section, and portions are omitted from the view clearly to disclose the construction.

In the present installation of mirrors for display orsimilar purposes, or for the purposes of effecting optical illusions, these mirrors are usually of large heavy sheets of plate glass supported in u right position. The weight of the glass 0 such IIllIIOIS is considerable. Consequently the mirrors will sag or bow of their own weight, thereby giving a distorted image. The usual stock size plate glass comes in thickness not greater than inch; which thickness of glass will bow considerable due to the weight of glass.

We have found, by experiment, that if sheets of plate glass two inches wide and of an inch thick, are each supported on knife edges spaced 23 inches apart and each sub ected to a 5 lb. weight placed midway between the knife edges, the average deflection is about .04 of an inch or 40 mills. Due to the great degree of bowing of mch glass, it is preferable to employ thicker glass to obviate distortion, where the glass is used as a large mirror. Generally, plate lass A of an inch in thickness is employed.

t 18 apparent that the cost of glass of such thickness is considerably greater than 1, inch glass. Furthermore, inch glass does not generally come in stock size; hence special orders must usually be placed for such size, increasing thecost and efiecting delay in se curing the desired thickness of glass.

Our invention is designed to obviate the above difiiculties; so as to permit the use of comparatively thin plate glass, in a mirror construction. Broadly, the invention comprises securing, to the glass mirror, a backmg plate of greater tensile strength than the mirror; so as to take up the tensional stresses which normally sheet glass is subjected to, by its own wei ht. Preferably spacing means is interposed etween the backing plate and glass sheet to provide a beam construction; the spacing means performing the important function of bringing the neutral axis of the beam away from the normal neutral axis of the plate glass, so as to lessen tensional stresses in the glass.

In greater detail and with reference to Figure 1, we employ plate glass 2 preferably inch in thickness, which is finished, accordin to usual practice, on one surface thereof to provide a mirror. To the finished surface of the glass is secured, by a coating 3 of any suitable adhesive, a spacing sheet 4. Any suitable material may be used as the spacing sheet, but we preferably employ fibreboard, inch in thickness, due to its lightness and the ease with which such material may be glued to the glass. For the fibreboard, any of the various com osition building boards on the market may used instead.

On the underside of fibreboard is secured by means of any suitable adhesive, forming an adhesive coating 6, the backing sheet 7 of greater tensile strength than the glass. Preferably, complaratively thin sheet metal is employed as the backing plate. We have found 16 gauge'sheet iron satisfactory.

By experiment, we have found that the avera e deflection caused by a 5 lb. weight, placeg on the glass surface of the mirror construction described and under the conditions previously set forth in connection with our,

experiments on 1 inch plate glass alone, is only .0045 of an inch, or 4 mills, in comparison to the 40 mill deflection of the plate glass alone. This deflection is approximately equal to the deflection of inch thick plate glass, under the experimental conditions described. It is hence apparent, that our mirror construction will permit the mirror to reflect as clear animage-as the inch plate glass. Furthermore, the Weight per square foot of the described construction is approximately 3 lbs. less than that of the inch plate glass. In the constructiondescribed, the neutral axis of the beam formed is without the body of the glass sheet; thereby relieving the glass of tensional stresses, in which it is weak. Although, we have chosen inch plate glass, 4 inch fibreboard and 16 gauge sheet iron, united in the manner described, for the purposes of illustratingour invention, the invention may be employed with any desired thickness of sheet glass, spacing s eet and backing plate, in accordance with the conditions desired. The spacing sheet may be omitted-abut if this is, done a heavier backing plate would have to be employed, thus increasing materially the weight of the construction.

By using the spacing sheet, the neutral axis of the beam is placed farther away from the normal neutral axis of the sheet glass and nearer the normal neutral ax s of the backing plate, thus lessening the tensional stresses in the glass, and allowing a thinner backing plate, to reduce weight. Furthermore, by using the proper thickness: of spacing sheet, depending on the glass thickness, the neutral axis of the beam may be brought without the bod :of the glass, as in the construction descri d. Y

A decided advantage of the described construction is the fact that when the mirror is, supported in upright position and a person or object should happen to bump the mirror, or bear, against it, there is no danger of the mirror breaking. Also, there is no danger of the mirror breaking, if it is set at an angle to the horizontal as is often done in effecting optical illusions.

In some cases, we' ,'have found that it is .unnecessarytoemplo'y a backing plate over the entire surface of, the mirror; and as illustrated in Figure 2, we may use spaced back ing strips 8, of the character described, adhesively secured to the fibreboard, spacing sheet 9, which may extend either over the entire surface, as shown; or which may be merely separate strips coextensive with backing strips 8. This construction obviously is of lesser weight than that shown in Figure 1. The backing strips 8 may be so spaced to produce the most efficacious results, depending on the glass thickness and the thickness of the spacing sheet.

As illustrated in Figure 3, we have shown a method by which our mirror construction may be advantageously secured in place and for the purposes of illustration we have chosen the modification of Figure 2. An aperture 11 is provided in the frame 12, the mirror construction being seated in groove 13 therein, and. framing 14 being provided about the edges of the mirror. In the aperture 11 and secured in any suitable manner, such as by welding to the fixed angle irons 16, are a plurality of supports 17. These supports are each preferably rods, united by a turnbuckle 18 of conventional construction. The ends of the supports, op-

posite to those secured to the angle irons, are secured, in any suitable manner, as by welding; to the metal backing plates 8.

y the described construction, the lengths of supports 17 may be so preadjusted by turnbuckles 18,. as to regulate the stresses in the mirror construction, and thereby compensate for any deflection and consequent distortion which might exist. Furthermore, the supports 17 provide additional reinforcmg means.

n Figure 4, is illustrated a modified arrangement, for supporting our mirror construction, in a wall 21; and for the purpose of illustration, we have chosen the modification of Figure 2; secured, in any suitable manner, to the backing'strips 8 adjacent the upper and lower edges of the mirror, isa metal truss 22. Supports 23, having turnbuckles 24, are secured to the truss and to the intermediate backing strips 8, in a manner described withrespect to theconstruction of Figure 3. The turnbuckles. 24 may be preadjusted to subject the mirror to the proper forces to insure against any deflection; and the entire construction may be re m'ovably positioned in the wall recess 26.

Although, in connection. with Figures 3 and 4, we have described themirror construc tion embodying the features of Figure 2,:it is apparent that the construction of Figure 1, where the backing plate is. coextensive with the surface of t e mirror, may be equally employed. a

Weclaim:' a 1. In a mirror construction, a backing plate of greater tensile strength than the mirror, and means integrally uniting said plate to'the mirror. 7 2. In a mirror construction," a .backing plate of greater tensile strength than the lit late to the mirror, includin spaced means interposed between the bac plate and mirror.

3.1n a mirror construction, a backing plate of sheet metal, and means into ally uniting said plate to the mirror, inclu ing a spacing sheet interposed between the sheet metal and the mirror.

4. In a mirror construction, a backing plate of greater tensile strength than the mirror, a spacing sheet adhesively secured to the backing plate, and a coatin of adhe-' sive securing the spacing sheet to t e mirror.

5. In a mirror construction a plurality of backing strips of greater tensile strength than the mirror, means adhesively secured to the strips for spacing them from the mirror, and means adhesively securing the spacing means to the mirror.

6. In a mirror construction, a backing plate of greater tensile strength than the mirror, means adhesively securing said backing plate to the mirror, and a support secured to the backing plate and to a fixed element to reinforce the construction.

7. In a mirror construction, a backing plate of greater tensile strength than the IHIII'OI', means securing'said backing plate to the mirror, and a sup ort secured to the backing plate and to a xed element to reinforce the construction, said support including a turn buckle for adjustlng the length thereof.

' 8. In a mirror construction, a plurality of backing strips of greater tenslle strength than the mirror, means securing the strips to the mirror, a plurality of supports secured to the strips and to a fixed element to reinforce the construction, said supports including turn buckles for adjusting the lengths thereof.

In testimony whereof, we have hereunto set our hands.

DAVID L. SHATTO. FRANK FLOYD LINDSTAEDT. 

